This invention relates generally to power rail constructions of the type adapted to be engaged by a travelling collector shoe, and more particularly to hangers for rails intended to be suspended along a wall or ceiling, as by means of a series of resilient metal spring clips.
In the past, a number of different hangers for rail constructions have been proposed and produced, having met with varying degrees of success.
Hung rails are generally suspended from support beams in the ceiling of a building or manufacturing installation by means of a series of generally U-shaped spring clips having a pair of leg portions which extend on opposite sides of the rail and a connecting web portion which is apertured to receive one or more bolts, by which the clip is secured to the ceiling beam.
A number of different variations of hangers for this basic structure have been employed in an effort to reduce the overall cost of the parts, and to simplify assembly. One of the problems associated with virtually all prior constructions was that due to the high labor charges that currently prevail, the cost of installation sometimes exceeded the cost of the components being installed.
Conductor rails are generally supplied with a channel-like insulating plastic sheath extending around the rail along three sides, with the mouth of the channel providing clearance for the travelling collector shoe. In one prior construction, the sheath was provided with oppositely disposed longitudinal ribs; these ribs were engaged by corresponding support teeth on the legs of the spring clip hanger such that the sheath normally rested on the sharp edges or ends of the teeth. Several problems with this construction became apparent. After a period of use, the plastic of which the sheath was constituted aged and became somewhat brittle. There was thus a likelihood of breakage of the ribs of the sheath in the event that an excessive transverse load was applied to the rail. In addition, hum and vibration of the rail tended to cause stress or fatigue of such ribs, possibly leading to cold flow or breakage. It can be readily appreciated that there was to be avoided a failure of the support mechanism for such rails, due to potentially serious injuries suffered by plant personnel who were inadvertently struck by falling rail sections, and the resultant liability of the owners of the plant facility.
In many cases the support provided to the rail was inadequate. In the constructions noted above, twisting of the rail tended to occur, thus unseating one of the ribs of the sheath from its support tooth. Where the rail was allowed to twist, problems arose, resulting from improper alignment with the travelling collector shoe, causing either erratic operation or failure, or both. Also, in many constructions there were no counter supports acting against the (upward) pressure of the collector shoe as the latter passed the location of the spring clip. Accordingly, the pressure of the shoe on the rail could not be maintained at a uniform level. Moreover, the approach of a collector shoe could give rise to an undesirable twisting of the rail, as noted above.
In another prior construction, the hook formations on the legs of the spring clip were received in undercuts in the sheath, to support the latter (and rail) and prevent pull-out. However, in some cases the rail could twist to such an extent that the one hook formation would become un-latched from the corresponding undercut, thereby resulting in pull-out of the rail. As noted above, constructions wherein an inadvertent release of the rail could occur were not considered satisfactory from the standpoint of safety. Prior patents showing some of the features described above are listed as follows: U.S. Pat. Nos. 3,995,725; 2,640,114; 3,316,362; 4,016,961; and 3,300,593.